This invention relates to piston type four cycle internal combustion engines and more particularly to a means for venting the clearance space behind at least the top compression piston ring to the crankcase of the engine during certain portions of the engine operating cycle thereby reducing hydrocarbon emissions from such engine.
U.S. Pat. No. 3,335,643, issued Aug. 15, 1967 to J. T. Wentworth discloses a method and means for reducing these unburned hydrocarbon emissions by the use of a ring design that seals the sides of the top compression ring and further provides a chamfer at the edge of the piston crown. Passages in this construction connect the crown of the piston with the ring back clearance to equalize pressures on the ring. This design, however, employs elastomeric or rubber sealing elements positioned on the top and bottom of the piston ring and there is some question whether this type of arrangement, and particularly the use of the elastomeric sealing members, would be feasible for large scale mass production engines that are used in the automobile industry.
U.S. Pat. No. 3,667,443 issued June 6, 1972 to Currie et al discloses an internal combustion engine that is provided with pistons having vent openings connecting the space between the first and second piston rings with the engine crankcase so as to vent to the crankcase gases rich in unburned hydrocarbons which escape from the combustion chamber past the first piston ring. It is stated in that patent that this method of venting the clearance space has been shown to reduce hydrocarbon emissions in some instances. It is stated in the patent, however, that the vent openings could be fitted with one-way valves.